French Pat. No. 1,390,405 (corresponding to U.S. Pat. No. 3,261,910) describes a stay insulator comprising two metal end pieces connected together by a tube having fiber glass wound around it to constitute a cylindrical sheet having part spherical caps at each end against which respective shoulders of the metal end pieces are brought to bear.
In order to improve the mechanical and electrical performance of such insulators, French Pat. No. 2,198,231 (corresponding to U.S. Pat. No. 3,839,593) proposes surrounding the part spherical end caps with a glass fiber binding. This solution has not been successful because cracking and unsticking have been observed between the binding and the caps due to their different temperature expansion coefficients. Proposals have also been made to fill the central tube with an electrically insulating fluid such as an insulating oil or sulphur hexafluoride to fill the cracks and to compensate for the temperature dilations and relative extensions due to conditions of use and to climatic conditions (wind, frost), inter alia.
Preferred embodiments of the present invention provide a composite type of stay insulator of simplified structure that avoids, in particular, the need to use an insulating fluid together with any sealing means and volume compensating means required thereby.